The present invention relates to an RF (=radio frequency) coil arrangement for an NMR examination apparatus, an object or target to be examined, e.g. a human body or some area of interest of a human body, being adapted to be placed inside said coil arrangement which is adapted to excite the nuclei of a selected target area by transmitting an RF field pulse substantially orthogonal to a homogeneous basic magnetic field produced by the apparatus and, thereafter, to receive and detect an NMR signal emitted by the nuclei in the target area.
It is well-known in the prior art that an NMR examination and imaging apparatus requires an RF coil, which on one hand transmits to a target a radio frequency pulse and thus exites a certain selected area of a target for mapping and, on the other hand, receives an electromagnetic field induced by nuclei precessing in said area, i.e. an NMR signal. These actions can be effected by means of a single RF coil or by using different coils for exciting and receiving. In so-called whole-body NNR mappings, in which one or a plurality of slices are imaged from e.g. the head or thorax of a patient, a homogeneous basic magnetic field is generally produced by means of solenoid coils with a patient pushed axially therein. A solenoid type of coil would in principle make also an excellent RF coil but in the present case it cannot be used since the field of an RF coil would then be parallel to the homogeneous basic magnetic field and deflection of nuclei from the direction of a basic magnetic field is not possible. For this reason, an RF coil must be provided by some other type of coil arrangement. In most commonly known equipment, use is made of a so-called a saddle coil arrangement, whose properties, however, are not equal to those of a solenoid since its configuration is more spatially distributed and since, due to the length of a conductor, the energy of a magnetic field is mostly distributed not in a target area to be imaged but elsewhere.
In order to overcome the problem, the publication EP-71896 proposes a solution based on the use of two saddle coils. Thus, it is possible to choose a magnetic field rotating in just one direction and leading to certain advantages, described in more detail later. However, the question is still about a saddle coil, whose other drawbacks are not eliminated by said solution. On the other hand, the publication EP-73375 discloses a solution that does not require saddle coils and likewise provides a possibility of detecting just one of the rotating directions. A weakness in this prior art solution is that it requires the use of an RF field-reflecting cylinder, which complicates the apparatus and adds to the costs.